Dsd is 15 and not a bad kid, she doesn't get into trouble and generally nice to be around. I know this is probably unreasonable expectations of a teenager but see what you think about this scenario...
She was here yesterday and her mum's partner phoned to tell her he was intending to propose to her mum today. Their extended families were also going to the house to celebrate. He asked dsd if she would like to be there too as he thought it would be nice. (she lives there but sometimes stays with us all day Sunday) As a bit of background, she gets on fine with mum's partner(with the usual family ups and downs) has a sibling from them and would have no issue with them getting married. Her response was " I told already that I have arranged to go to xxxx with my friends, then we are all going to xxxx."
Now, I understand that she had made prior arrangements and that it was last minute but she didn't say how much she would have liked to have been there, just criticised him for not remembering her plans (nothing that she couldn't do every week). I gave her a couple of suggestions which may have made her lose half an hour to an hour of time with her friends - she wasn't interested. Dh and I pointed out that this was an important time for her mum and she would want her there if she could be. We both said we weren't angry with her but we felt she had made the wrong choice but it had to be up to her.
I know teenagers are selfish but it was the total lack of care for anyone else's feeling and her complete inflexibility that irritated us.